I've worked in this industry a long time now.
From 1981 to 1986, I worked as an engineer for Hewlett-Packard. Yep, I'm "have actually met both Bill Hewlett and Dave Packard" old. They'd retired when I met them and John Young was in charge, but they came to Palo Alto to a shareholders' meeting and I was there at the time.
Most of my work was on HP3000 commercial mini-computers. The level of engineering on those systems was unlike anything I'd ever seen either before or since. They were really quite superb.
And one thing that I worked on a lot, was hard drives. HP were constantly at the bleeding edge on really reliable drives for commercial systems.
So what's that got to do with spinning rust?
I keep hearing people talk about "spinning rust" when they're referring to spinning hard drives, often to separate them from SSDs. And it always sounds so very strange to me.
I worked on "spinning rust" and know full well what it was like. Originally they weren't hermetically sealed drives like today, so it was obvious to anyone working on them what was in them. Many were also removable so that made it even more obvious. But later after Winchester style drives became common, they all started to be sealed up, where users couldn't see inside them.
Somewhere, I'm guessing around 1984 or 1985, the coating on the platters changed. The old oxide coatings (i.e. rust as most people know it) that were used gave way to magnetic coatings that resembled mirrors. And typically it was coated over a non-magnetic material, often aluminium(on older drives) or even ceramics. But most drives you'd come across today commonly use glass as the substrate. Toshiba pioneered that back in 1990.
So the disks in your spinning hard drives are super-shiny mirrors.
It'd make far more sense to refer to "spinning mirrors" than "spinning rust".